Epidemiologic studies have found an association between short-term increases in particulate air pollution and cardiovascular morbidity and mortality. Our Program Project goal is to understand the relation of particle pollution to clinical, physiologic and biochemical endpoints reflecting potential mechanisms underlying these associations. In this Research Project we have focused on endpoints influenced by autonomic regulation. We have found that short-term exposure to ambient air pollution is associated with increased risk of ventricular arrhythmias in patients with Implanted Cardioverter Defibrillators (ICD). Although the study was not originally designed to detect supraventricular arrhythmias, we found the risk of these events also was associated with air pollution episodes. Improvements in ICD diagnostic capabilities have increased their utility for such studies. Most current ICDs have dual chamber monitoring, allowing more specific definition of ventricular versus atrial tachyarrhythmias. A growing number of Coronary Resynchronization Therapy ICD devices are being implanted in congestive heart failure patients, a group particularly susceptible to sudden death from arrhythmias. We propose to enroll 400 Boston area patients with dual chamber ICDs being followed at Tufts-New England Medical. We will prospectively follow these patients for an average of three years recording confirmed episodes of acute ventricular and supraventricular tachyarrhythmias, with improved definition of our arrhythmia outcomes. Using case-crossover methods, we will assess the risk of ventricular and supraventricular tachyarrhythmias with ambient air pollution concentrations in the hours and days prior to these arrhythmias. Enhanced pollution exposure monitoring will enable us to characterize differentiate effects of particle components, with improved assessment of spatial as well as temporal differences in exposure. Finally, we will assess if this risk is greater in susceptible subgroups including patients with elevated systemic inflammation, depressed vagal tone, or a diagnosis of congestive heart failure.